Large scale refrigeration systems in which a refrigerant is chilled in the liquid form by self-evaporation in stages are well known. The self-evaporation is effected by pressure lowering suitable expansion valves into vapor liquid separators and the vapors compressed back up to condenser pressure. As the operation involves adiabatic expansions, the increase in entropy is quite marked and hence, of course, the power required is greater and efficiency is less. With ammonia as a refrigerating element, it is difficult to achieve efficiencies, over theoretical completely reversible Carnot cycles, of significantly more than about 50%. Thus while the self-cooled liquid systems are extensively used for large scale refrigeration, there is still a substantial power cost; and therefore the systems, although practically useful, leave considerable to be desired from the standpoint of power consumption and efficiency. It is with an improved refrigeration system of the self-cooling liquid type but with improved efficiencies that the present invention deals.